Highly selective fluorimetric and colorimetric sensing of mercury(II) by exploiting the self-assembly-induced emission of 4-chlorothiophenol capped copper nanoclusters.

A highly stable copper nanoclusters (CuNC) carrying 4-chlorothiophenol as a protective ligand is described. They display self-assembly-induced emission with excitation/emission maxima at 330/605 nm even in neutral or alkaline aqueous environment. The fluorescence of these CuNC is quenched by Hg(II). Quenching is mainly ascribed to the formation of a complex formed via Hg-S bonding between the Hg(II) ions and the ligand. This destroys the ordered architectures of the assembled CuNC. The assay enables Hg(II) to be determined with good sensitivity and a linear response ranging from 1 to 500 nM Hg(II) with a 0.3 nM limit of detection. In addition, the method was implemented in a test strip (which undergoes a color change from red to blue) that can be used for visual determination of Hg(II) in complex environmental water samples. Graphical abstractNovel and highly selective fluorimetric and colorimetric methods have been designed for mercury(II) ions determination based on stable self-assembly-induced emission of copper nanoclusters.

Poly(adenine)-templated fluorescent Au nanoclusters for the rapid and sensitive detection of melamine.

A rapid and label-free fluorescence sensing strategy has been established for the sensitive determination of melamine (MA) on the basis of poly(adenine) (poly (A))-templated Au nanoclusters (AuNCs). The poly(A)-templated AuNCs possessed excellent luminescence and photo-stability. In the presence of Hg2+, the luminescence of AuNCs was quenched by Hg2+ through the metallophilic interactions between Au+ and Hg2+. When melamine was introduced, the fluorescence intensity of sensing system could be recovered. There was a greater coordination interaction between Hg2+ and melamine, which blocked the Hg2+-mediated fluorescence quenching of AuNCs. The assay allowed sensitive determination of melamine with a linear detection range from 50 nM to 100 µM. The limit of detection was as low as 16.6 nM. Furthermore, the label-free strategy was successfully employed for the detection of melamine concentration in real samples.

DNA-templated Au nanoclusters coupled with proximity-dependent hybridization and guanine-rich DNA induced quenching: a sensitive fluorescent biosensing platform for DNA detection.

In this paper, the fluorescence signal of poly(A) DNA-templated Au nanoclusters (AuNCs) is found to be greatly quenched by photoinduced electron transfer (PET) when they are close to guanine (G)-rich DNA. Based on the findings, we have designed a low-cost fluorescence biosensing strategy for the sensitive detection of DNA. Highly luminescent and photo-stable poly(A) DNA-AuNCs were utilized as the fluorescent indicator and G-rich DNA was utilized as the fluorescent quencher. In the absence of target DNA, DNA-AuNCs failed to hybridize with the G-rich DNA and did not form the duplex DNA structure. Strong fluorescence intensity at 475 nm was observed due to the DNA-AuNCs being far away from the G-rich DNA. However, in the presence of target DNA, the DNA-AuNCs together with G-rich DNA could hybridize with the target DNA, leading to the 5' terminus of the DNA-AuNCs and the 3' terminus of G-rich DNA being in close proximity and promoting the cooperative hybridization. Therefore, a "Y" junction structure was formed and the G-rich sequences were brought close to the AuNCs. Therefore, the fluorescence intensity of the sensing system decreased significantly. Taking advantage of the poly(A) DNA-templated Au nanoclusters and G-rich DNA proximity-induced quenching, the strategy could be extended to determine other biomolecules by designing appropriate sequences of DNA probes.